Pulverized fuel burner



Jan. 11, 1949. F. T. HAGUE PULVERIZED FUEL BURNER Filed June 6, 1946INVENTOR FL. ova T. Haqu:

BY. W M

WITNESSES! 5 TH 1M5 7?}6'777: e o-17 ATTORNEY rv y nsjrznnmt st m 1*Floyd T.-Hague, llr'exel Hill, Pa asslgnor to Welt-R lnghou'se ElectricCorporation, East Pittsburgh,

Pa... a corporation of Pennsylvania Application June 6,1948, Serial No.574,134

3 Claims. (01. 110-28) This invention relates to combustion apparatus,more particularly to combustion apparatus for pulverized fuel, and hasfor an object to provide improved apparatus of this character.

In studies of pulverized fuel firing, it has been found that when usinga medium volatile coking coal the incoming fuel particles, under theinfluence of furnace temperature, are blown'up into cenospheres byescaping volatile matter. A cenosphere is defined as an empty orv hollowsphere, ball or-globe. Consequently, it has been concluded that thetemperature and rate of tem perature rise in the region just ahead ofthe zone of ignition should be maintained as high as possible. Contraryto previous assumptions, the fuel particles in the form of cenospheresburn essentially at constant diameter, leaving a very fragile,highly-perforated, lacy structure, which is usually broken intofragments in the flnal stage of combustion. The more rapid the rate oftemperature rise in'the region just ahead of the zone of ignition, themore violent is the break-up of the cenospheres into small sizedparticles and the finer is the resultant fly ash.

To obtain this desired high temperature and high rate of temperaturerise in the region just ahead of the zone of ignition, the presentinvention provides for strong axial counterflow, bringing the hottestfurnace gases back to the center of the burner to heat up the incomingfuel and air streams. This counterfiow of the hottest furnace gasesinsures burner stability and early ignition of the mixing fuel and airstreams as well as effectiveproduction of the smallest possible fly ashparticle'slze, as explained in the first part of the precedingparagraph.

The strong axial ccunterflow discussed above is, in turn, dependent uponhigh swirl velocity of the fuel and/or air streams, and to obtain swirlvelocities of suitable values, the present invention provides forintroduction of the "fuel and air to the combustion chamber in a novelmanner. Conventional burners usually introduce the airborne fuel in thecenter of a swirling secondary air supply core, and thefuel'is graduallydispersed or diffused throughout this secondary air stream. This gradualdiffusion of the fuel into the secondary air stream takes a measurabletime,

and the observation of a burner of this type shows The presentinvention, on the other hand, provides an annular series of nozzlevanes, through 'alimited number of which the airborne fuel is admitted,the secondary air entering through the remaining nozzle vanes of thisannular series.

.Various ratios of fuel nozzle vanes to secondary air nozzle vanes maybe used, and a ratio of approximately nine secondary air nozzle vanesfor eachfuel nozzle vane has been found to be satisfactory for generalpurposes. For example, with a half ton per hour burner, sixty nozzlevanes may be employed; six of these admitting airborne fuel and theremaining fifty-four admitting secondary air. The limited number of fuelnozzle vanes will be uniformly spaced in the annular series of nozzlevanes, and in the example mentioned, each of the six fuel vanes will bespaced sixty degrees apart, with nine Secondary there is little radialcomponent of flow of fuel and secondary air from the vanes to the innerwall of the combustion chamber, which wall confines the swirlingcylinder of fuel and air. Consequently, little of the swirl velocity isdissipated in radial expansion and the .axial component of flow of theswirling stream is thereby maintained at a maximum. Likewise, the swirlturbulence is maintainable for the maximum axial-distance, usually forthe full length of the combustio chamber. I

Therefore, another object of the invention is to provide early .mixingof fuel and air streams in pulverized fuel combustion apparatus.

Yet another object of the inventionis to provide high swirl velocity inthe fuel and air streams of pulverized fuel combustion apparatus.

A further object of the invention is to provide a high degree of fueland air swirl turbulence in pulverized fuel combustion apparatus.

Another object of the invention is to provide maintenance of high swirlturbulence throughout the length of the combustion chamber of pulverizedfuel combustion apparatus.

An additional object of the invention is to proinvention as will beapparent from the following description and claims taken in connectionwith the accompanying drawings, forming a part of this application, inwhich:

Fig. 1 is a longitudinal sectional view of combustion apparatusembodying the principles of the present invention;

Fig. 2 is an elevational view of the downstream or discharge end of thefuel nozzle or burner of Fig. 1, and showing the disposition of thenozzle fuel vanes relative to the nozzle secondary air vanes; and

Fig. 3 is a sectional view, taken along the lines III-III of Fig. 1,looking in. the direction indicated by the arrows.

Referring now to the drawings more in detail, the reference character Iindicates, in its entirety, combustion apparatus comprising a furnace llhaving front and rear end walls l2 and I3, respectively, joined by asidewall II which may be of circular or non-circular cross section.

These walls are herein illustrated as of brick, but

it will be apparent that any suitable material may be utilized, forexample, cast iron or steel. The walls l2, l2 and I4 define a combustionchamber It to which both fuel and air are supplied by the burner l1,located centrally of the front wall l2,-and whose novel construction andoperation are now to be described.

The burner l'l comprises a cylindrical inner casing is to whichfinely-pulverized fuel (for example, coal) is borne through the conduitII by a stream of primary air. An outer casing 2|, of materially greaterdiameter than the inner casing l8, surrounds the latter in concentricrelation, secondary air being introduced to the annular space 22 betweensaid inner and outer casings by the conduit 22.

In order to distribute the flow of secondary air uniformly through thevarious sections of the annular space 22, the latter is provided withnumerous partitions 2l,extending radially between the inner and outercasings l8 and 2! preferably in uniformly spaced relationcircumferentially of said annular space, and defining, with the innerand outer casings l8 and 2|, segmental nozzle passages 26 (Fig. 2)through which the secondary air from duct 23 passes to enter thecombustion chamber l8. 7

To obtain uniform mixing of the pulverized fuel and secondary airimmediately upon entry thereof to the combustion chamber, the airbornefuel is diverted radially from the, downstream end of the inner casing18 into a limited number of segmental fuel nozzle passages 21,ilnterspersecl among the remaining air nozzle passages 26, andpreferably being uniformly spaced circumferentially of the annularseries of nozzle passages.

In the arrangement illustrated in Figs. 1 and 2, four fuelnozzle's 21are uniformly dispersed among twenty-four secondary air nozzles 2|,communication' between the interior of the inner casing II and the fuelnozzles 21 being effected by openings 28 provided in the inner casing itat locations aligned with the fuel nozzle segments 21 (Fig. 1). All ofthe airborne fuel delivered to the inner casing I8 is forced to flowthrough the openings 28 into the communicating fuel nozzle segments 21,since the downtream end of casing It is blocked by the end wall 29-.

The fuel nozzle segments 21 pass only airborne fuel from the innercasing l8, entry of secondary air thereto from the conduit 23 beingprevented by closure walls 3| extending diagonally of the fuel nozzlesegments 21 (Figs. 1 and An annular series of inclined vanes 32 isprovided adjacent the outlet or downstream end of the annular series offuel and air nozzle passages 21 and 26, the vanes extending radially andall being inclined in the same direction to impart swirling action tothe air and fuel streams entering the combustion chamber I6. Preferably,these vanes 32 are secured to, or formed integral witht'the exit edgesof the partitions 24 separating the nozzle passages 26-21 (Figs. 1 and3).

Preferably, these vanes are of the type used in steam turbinediaphragms, which are recognized to be about 98 per cent eflloient. Itis believed that nozzles of this type have never before been used inapparatus of the character concemed with here.

In operation, airborne pulverized fuel is supplied through the conduitl9 to the burner I! where it enters the fuel nozzle passages 21 throughthe openings 28 in the inner casing l8. Simultaneously, secondary air,supplied through the conduit 23, enters the alrnozzle passages 26, andboth air and fuel, emerging from the'nozzle passages 26-21, enter thecombustion chamber IS with a swirling motion imparted thereto by theinclined vanes 22, this swirling action continuing throughout the lengthof the combustion chamber. This high swirl velocity of the fuel and airstream within the chamber sets up a strong axial counterflow of hotgases from the rear end of the chamber, which flow occurs from the reartowards the front of the chamber along the axial center thereof, asindicated by the arrows A of Fig. 1.

' This strong axial counterflow brings'hot gases to the inlet end of thechamber where they produce' both high temperatures and high rate oftemperature rise in the entering stream of fuel and air. These hightemperatures and high rates of temperature rise provide both earlyignition of the swirling fuel-air stream and maximum size reduction ofthe fuel particles incident to their transformation to cenospheres, aspreviously discussed.

No attempt has been made to illustrate any particular type ofheat-utilizing means in association with the heat-producing apparatusherein disclosed, as it will be apparent that the novel combustionapparatus will have utility with numerous types of heat-utilizingapparatus. If the combustion apparatus of the present invention were tobe utilized in connection with a steam boiler, the tubes of such boilermight well be positioned in the downstream or rear portion of thecombustion chamber IS, the products of combustion passing through theoutlet openbe conducted through the outlet opening 36 to a gas turbine,or other heat-utilizing apparatus.

While the invention has been shown in one form, it will be obvious tothose skilled in the art that it is not so limited but is susceptible ofvarious changes and modifications without departing from the spiritthereof.

What is claimed is:

1. In a pulverized fuel burner, inner and outer concentrically-disposedannular casings defining therebetween an annular nozzle chamber, radialpartitionsseparating said annular nozzle chamber into a plurality ofnozzles, means for supplying airborne fuel to the space within the innercasing, means for supplying secondary air to certain of the nozzles,means for admitting airborne fuel from the interior of the inner casingto the other of the nozzles, and means preventing entry of secondary airto said other nozzles.

2. Structure as specified in claim 1, including means for impartingswirling motion to the fuel and air leaving said nozzles.

3. In a pulverized fuel burner, wall structure said nozzles, means forsupplying air to the remainder of said nozzles, and means for convertingr the pressure energy of the fuelianduairwithin defining an annularnozzle ring, means dividing said ring into a plurality of nozzles, meansfor supplying pulverized fuel to alimited number of the nozzles intovelocity energy adjacent and before the nozzle exits and for imparting aswirling motion to the fuel and air, said last-mentioned 9 meanscomprising an annular row of steam turbine diaphragm type vanes.

FLOYD T. HAGUE.

REFERENCES CITED The following references are of record in the file ofthis patent:

